The bane of upper elementary math! One of the most difficult concepts to teach in math is subtracting across zeros involving 3 or more digits (even subtracting across 2 digits may present an issue). I've tried it all. Having used manipulatives (a "concrete" teaching strategy) for years now, I can attest that they only work for those students that already "get it". Even attempting to write this poster proved how difficult this concept is to explain, regardless of how much it's second-nature for a